In certain types of image processing systems, especially color correction systems employed in post-production equipment, system operators observe an image on a video monitor, adjust color and other parameters of the image until it is aesthetically satisfactory, store the parameters in system memory, and apply the parameter corrections to a sequence of images forming a scene. Various types of image processing are often employed to create, enhance, compress, filter, or otherwise modify characteristics of an image.
In a video signal color correction system, color corrections of motion picture film and/or video tape are typically made on a scene-by-scene basis. A "scene" is a sequential collection of images shot from the same camera, having the same viewpoint, composed in a certain way, etc. A system operator or "colorist" views a selected exemplary image or frame from a scene. The colorist then applies color corrections via a control panel to adjust video parameters such as hue, saturation, luminance, etc. of a frame image being viewed. The correction settings are stored in system memory.
After the colorist is satisfied with the adjustments he or she has made to the selected frame, the correction system, which is typically computer-controlled, applies the stored color corrections to each frame in the scene one at a time. The color-corrected frames of the scene are then recorded on film or videotape. The steps are repeated for other scenes in the film or video tape, often with different correction settings stored for different scenes. This process creates a color-corrected master film or video tape that reflects color adjustments to all frames in all scenes.
Devices are known in the art for defining a region of an image for applying one set of color corrections, with other regions of the image receiving another, separate set of color corrections. Such devices are useful when it is desired to isolate a certain area of an image to receive special image processing. For example, in color correcting a soft drink commercial it may be desirable to isolate the beverage can from the remainder of the image so as to make the colors of the beverage can stand out from the rest of the image.
U.S. Pat. No. 4,710,800 to Fearing et al. describes an apparatus for allowing operator selection of a color region of a video image based on color. The patent describes a system for generating and positioning a cursor on a video monitor to allow selection of a color region as defined by a particular hue as opposed to a geometric region. Circuitry responsive to the cursor location selects one of a plurality of color correction circuits to become operative for directing video parameter corrections such as hue, saturation, and luminance only to regions in the video image corresponding to the hue selected by the cursor. This system therefore allows application of image processing, namely color correction, to all regions of the image bearing the color that was selected with the cursor. While this system is suitable for allowing delineation of regions for receiving image processing based on color, it does not operate on the geometry of regions.
U.S. Pat. No. 4,782,384 to Tucker et al. describes a video parameter control system operative for selecting a spatial region or window in a video image for correction. A track ball allows selection of a spatial region by dragging a cursor to draw a window around an object of interest in the picture. The operator then adjusts controls that affect only the selected window or region. A first set of correction signals is stored for the selected region, and a separate second set of correction signals is stored for areas of the picture outside the selected region, thereby allowing multiple sets of corrections for a given frame. Although the Tucker et al. patent provides some teaching regarding movement of the window over a plurality of frames to effect a dissolve, the region is essentially static and the geometry is invariably that of a box.
Certain prior art image processing computer software, e.g. ADOBE PHOTOSHOP.TM., manufactured by Adobe Systems Corporation, Mountain View, Calif., employs edge detection algorithms for detecting color regions and creating paths or Bezier curves between points. Such edge detection algorithms rely upon color differences between regions to define the paths and produce odd results if there are discontinuities in the edges of a region, or if the colors defining the regions are not sufficiently dissimilar. The PHOTOSHOP.TM. software, for example, vectorizes an entire color region and provides no control over the number of points in the region. There is no way to modify a defined region except by changing region qualification parameters. For these and other reasons, this software is not suitable for real time applications such as a scene by scene color corrector.
Image region selecting capability known as the "Simple Windows" and "Power Windows" features are extensions of the foregoing Tucker et al. system. These features are provided in the RENAISSANCE 8:8:8.TM. digital color enhancer system, manufactured by the assignee of the present invention. In the Simple Windows feature, a window is a predetermined regularly shaped area or region of the video image that can be varied in size. The colors within the window are independently adjustable from the colors of the rest of the image. Primary or secondary color enhancements can occur both inside and outside a window, and each adjustment is independent of the other. The Simple Windows feature entails use of a simple geometric form--a square or rectangle--for a window shape. A Simple window is always rectangular and is defined by four points. Lines defining the window are always straight vertical or horizontal. Furthermore, there are no soft edges, that is, there is a sharp delineation between the inside and outside of the window, which sometimes produces undesirable image effects at the boundaries.
The more recent "Power Windows" feature provided more choices of the shape for the window, for example, circular, rectangular, half screen, split in the middle, etc. Windows comprising multiple squares, multiple diamonds (essentially rotated squares), horizontal and vertical bars, circles, ellipses (a warped circle), etc. can be selected by the operator. The sizes of these windows could be varied as long as the shape remained regular. Furthermore, a "soft edges" feature was provided so as to provide a gradual transition in color correction from the inside to the outside of the selected window. Power Windows, however, are still confined to regular shapes, with predefined geometry.
Many prior art systems do not effectively handle a "dissolve", where the region of interest changes in size, shape, location, and/or geometry over several frames in a scene. An object or area of interest often moves around in an image or changes geometry during a number of frames in a scene. For example, consider the case of a bottle and a glass in a scene where only the color characteristics of the bottle are desired to be adjusted. During the scene, the bottle (viewed from the side) is lifted from an initial upright position to a tilted position, rotated so that the mouth of the bottle is facing the viewer, moved toward the glass, and poured into the glass. In this scenario, the geometry of the bottle--the overall outline--changes from essentially a side view of the bottle (an irregular shape) to a top view of the bottle (a round shape). The bottle, which is not a "regular" shape, also changes in location and size.
Prior art systems that allow the definition only of predefined geometric areas are incapable of defining regions that move and change size and geometry with respect to a number of frames in a scene. Moreover, most objects in the world are not regularly shaped in the sense of being only rectangles, circles, etc. Accordingly, there is a need for a system that allows definition of an arbitrarily shaped window in accordance with a region of interest in an image, and that provides the capability for that region of interest to move as well as change size and geometry over a plurality of frames.